My son is not quite 3 years old yet. He's doing great in terms of speaking except for one detail: whenever a word begins with an s he will just skip that sound. For instance he consistently says top instead of stop.

When the s is in the middle or at the end of a word, he always says it correctly.

He's being raised bilingual (Danish and German) and can say rather long sentences clearly enough that strangers understand him. Clearly he has no problems with learning to speak in general -- it's just this s that's weird.

I don't know if it's common, but both my siblings (swedish) did this. My sister had problems with "s" until she was around 3, and then it stopped. My brother also did it, but with the letter "F". For him, it didn't go away by itself, so he had to see a speech specialist and managed to start saying "F" correctly around 6. I don't think it's something you need to worry about this early on, but maybe check with your pediatrician next time you're in for a development check?
–
Mia ClarkeSep 2 '12 at 14:57

My 3½ year old son, although understood well in both languages to a stranger (raised in English and Slovak), is replacing some sounds. He cannot pronounce ch-ange, whi-ch, or similar - but rather uses s. It is consistent in both languages. As he is improving, although slower than I have expected, I haven't decided to visit specialist yet.
–
Matej KovacSep 2 '12 at 19:03

My name begins with an S, and my 2.5 year old daughter still skips the s. She does the same thing with "(s)top" (like yours), etc. Seems common.
–
SwatiSep 3 '12 at 1:50

I had a problem with my ears growing up and mispronounced words sometimes. I could speak normal enough to where my parents didn't think anything of it for a while. They took me to have hearing tests and I passed them. I remember watching the tester and if they looked left and their left arm moved I knew to raise my left hand, same with the right side. Finally after a while they took me to a specialist and he had me face away from the tester, I failed almost instantly. They put tubes in my ears and now I have better hearing than most. You might want to get him checked.
–
BillyNairSep 3 '12 at 17:38

1

I was just about to post this same question. My 2y3mo son has trouble with the initial s, but can make an s sound. I am reassured that he's not the only one.
–
Kit Z. FoxSep 8 '12 at 2:05

I can tell you that my 2.5 year old has the same issue. Maybe it's also related to the bilingual issue as he's been raised speaking Hebrew and English (and since Hebrew also has some of the German sounds - maybe that's the effect).

For example, he keeps complaining that he (s)lipped and got a (s)cratch on his knee. If I try to get him to say scratch - he'll do it but the next time it'll just be another cratch.

We tend to think of letter sounds as distinct, but linguists break them down into their constituent mouth/tongue/throat/lip movements. So 'aah' is just a simple throat vocalization, 'Da' is the same but with the motion of opening the mouth with the tongue. A number of sounds are like this that require little in the way of mouth muscle movement and for that reason are ones that most children exhibit early.

Other sounds require more complex movements or coordinated actions, and because of that can be harder for the child to master. l, s, r, v, z, ch, sh, th (mentioned in William Grobman's answer) are all good examples. Think about how your mouth moves when making these sounds.

My 3-year old has similar pronunciation difficulties with letters that require tongue movements, and he drops or fudges letter sounds like t, s, z, sh. (I myself had s troubles well into 1st grade.) My 1-year old daughter on the other hand seems to do quite well with tongue-based sounds but doesn't say many 'lip' sounds like m and p.

I figure each child kind of follows their own path in mastering the different mouth movements. Some they pick up automatically on their own, others they may need extra coaching on. I go about this by playing tongue mimicking games with my son (as teachers did with me), to help him learn the muscle movements that the more complex letter sounds depend on. But I figure he's still got a couple years before he needs to get them all down so don't worry about it too much.

In addition to other good answers here, I can also add that the child will more easily learn sounds that are mainly formed by the visible part of the mouth. I have often seen my 2-year old studying my mouth when I speak, as if he's trying to figure out how I'm making the different sounds. Then afterwards, he is repeating some words to himself after I left.